Feasibility of the scheme for the abdominal gemstone spectral CT angiography with a low-concentration contrast medium

Objective: To explore the feasibility and application value for the abdominal gemstone spectral CT angiography (CTA) with a low-concentration contrast medium. Methods: Three hundred and thirty two patients underwent the abdominal spectral CTA at our hospital during March to December, 2013 were collected prospectively. According to the concentration of contrast medium, two protocols were made as below. In group A, an individualized low concentration of contrast medium was set as 270 mg/ml; in group B, a routine high concentration of contrast medium was set as 350 mg/ml. Two groups were further divided into 3 sub-groups according to the scanning parameters of different BMIs: sub-group A1 and Bl (BMI ≤ 22 kg/m²); sub-group A2 and B2 (22 kg/m² < BMI ≤ 25 kg/m²); sub-group A3 and B3 (BMI > 25 kg/m²). All scans were completed on Discovery HDCT. The tube voltage of A1 was 80 kVp, 50% adaptive statistical iterative reconstruction (ASIR) was used to reconstruction. The tube voltage of A2 was 100 kVp, 50% ASIR. A3 underwent gemstone spectral imaging (GSI). In group B, a routine tube voltage(120 kVp) was used, filter-backproject (FBP) was used to reconstruction. In each sub-group, the dose of (contrast medium were same (100 ml). The image quality at the abdominal aorta and its branch (right renal artery) in every sub-group were scored. The CT values at the renal hilum horizontal abdominal aorta in 6 sub-groups were measured, the CNR and FOM at the abdominal aorta were calculated. CTDIvol was recorded, total amount of iodine were compared. Between three corresponding sub-groups (i.e. A1 Vs Bl, A2 Vs B2 and A3 Vs B3), the image quality at the abdominal aorta was compared with rank-sumtest, and the abdominal aorta CT value, CNR, FOM, CTDIvol through the independent t test. Results: Finally 328 patients were included in the study, 169 cases in group A with 78 in A1, 30 in A2, 61 in A3. One hundred and fifty nine in group B with 63 in Bl, 35 in B2, 61 in B3. The score of the right renal artery in Al, A2 and A3 was 4.59 ± 0.52, 4.16 ± 0.65 and 4.13 ± 0.69, respectively. And the score in Bl, B2 and B3 was 3.70 ± 0.69, 3.91 ± 0.70 and 4.18 ± 0.66, respectively. The score in A1 was higher than B1(Z = -7.04, P < 0.01). The CNR in Al, A2 and A3 was 18.35 ± 3.66, 14.12 ± 2.78, 20.10 ± 6.96, respectively; in Bl, B2 and B3 was 12.02 ± 3.01, 11.82 ± 2.77, 13.32 ± 2.84, respectively. The FOM in Al, A2 and A3 was 68.28 ± 33.78, 30.41 ± 10.87, 26.78 ± 17.76, respectively; in Bl, B2 and B3 was 18.08 ± 9.05, 14.21 ± 7.12, 11.72 ± 7.40, respectively. Both the CNR and FOM were significantly higher in group A than that in group B (P < 0.01). The CTDIvol was (5.48 ± 1.33), (6.87 ± 1.39) and (16.87 ± 0.00) mGy in Al, A2 and A3, respectively, and CTDIvol was (9.12 ± 2.87), (11.02 ± 3.28) and (18.47 ± 5.84)mGy in Bl, B2 and B3 respectively, at a decrease by 39.91%(3.64/9.12), 37.66%(4.15/11.02) and 8.66%(1.60/18,47) between the corresponding sub-groups respectively.In the group A and B, the total amount of iodine was 27000 mg and 35000 mg respectively, at a decrease by 22.86%(8000/35000). Conclusion: With low concentration contrast medium, using optimization protocol according to BMI can decrease radiation dose without sacrificing image quality. (authors)